Long-Term Mechanical Stabilization of the Nanoscale Optoelectronic Properties of Halide Perovskites for Indoor PV Applications: SPM and DFT Investigation.

The stability of nanoscale photovoltaic halide perovskite devices is essential for their practical implementation in renewable energy applications. However, charge carrier trapping, recombination, and defects, such as halide or vacancy migration, suppress the stability of halide perovskites under operational or environmental conditions. In this work, we investigate mechanical treatment to mitigate phase segregation and ion migration by controlling the grain boundary (GB) structure and physical properties over long time scales of up to a year. We show that this treatment modifies the grain boundary structure from a defective to a closed configuration. Employing scanning probe microscopy techniques, we further analyze the impact of humidity over a one-year duration on nanoscale photovoltaic behavior. Our findings indicate that the mechanically processed samples preserve better morphology and optoelectrical properties for extended periods, demonstrating the effectiveness of engineering the GBs in enhancing photovoltaic device stability. DFT calculations reveal that engineering the GB structure from open to closed GBs leads to a reduction in the activation energy for ion and vacancy movement, resulting in slower vacancy migration in the closed GBs sample. Closed GBs samples exhibit higher elastic and mechanical properties than open GBs samples. Our insights will be helpful for designing halide perovskite-based devices with enhanced functionality and improved environmental stability.